The flight crews were certified and qualified for the flight in accordance with existing regulations. The weight and centre of gravity of each aircraft was within prescribed limits, and each was maintained in accordance with existing regulations. Although the Cessna 150's pilot was arriving from the south, he had bypassed the airport in a long detour to the east in order to approach the airport on the north side to join the Runway 29 circuit. He thus followed in every respect the procedure for joining the circuit of an uncontrolled aerodrome, just as the Cessna 172 was following the procedure for continuous circuits. Furthermore, the aircraft reported where they were supposed to as set out in CARs 602.101 and 602.102. The pilot of Cessna 150 C-FNLD knew that another aircraft was ahead of him and probably decided to stretch out his downwind leg to give this aircraft time to touch down and clear the runway. The crew of Cessna 172 C-GEYG did not stretch their downwind leg to follow the aircraft ahead; the crew may have confused the Cessna 150 C-FNLD, still in the circuit, with the traffic that had just landed, or else was not attentive to the communications that would have allowed them to know what aircraft were ahead. The crew of each aircraft could have seen the other aircraft at several places in the circuit. The pilot of Cessna 150 C-FNLD could have seen Cessna 172 C-GEYG at turning on the base leg and after his turn on the final leg. The pilot of Cessna 172 C-GEYG could have seen Cessna 150 C-FNLD while C-GEYG was on the downwind leg and during its descent on the base leg. Several factors, such as the appearance of the aircraft, the environment, a lack of attention or operation of the radios, could explain the collision, but no single factor could be identified in the investigation. The lack of evasive action by either aircraft indicates that neither aircraft had noticed the other. The landing light of Cessna 172 C-GEYG was on, thereby increasing the possibility of its being identified by Cessna 150 C-FNLD during certain phases of flight. This advantage, however, proved useless when the aircraft were on the final leg, because Cessna 172 C-GEYG was behind and above the Cessna 150. The aircraft collided in flight at an altitude of 450 feet on the final leg for Runway 29 at Mascouche and crashed, although, just before the collision, a pilot on the ground tried to warn them of the danger. The video sequences show that when the aircraft separated there was insufficient altitude available to effect a recovery.Analysis The flight crews were certified and qualified for the flight in accordance with existing regulations. The weight and centre of gravity of each aircraft was within prescribed limits, and each was maintained in accordance with existing regulations. Although the Cessna 150's pilot was arriving from the south, he had bypassed the airport in a long detour to the east in order to approach the airport on the north side to join the Runway 29 circuit. He thus followed in every respect the procedure for joining the circuit of an uncontrolled aerodrome, just as the Cessna 172 was following the procedure for continuous circuits. Furthermore, the aircraft reported where they were supposed to as set out in CARs 602.101 and 602.102. The pilot of Cessna 150 C-FNLD knew that another aircraft was ahead of him and probably decided to stretch out his downwind leg to give this aircraft time to touch down and clear the runway. The crew of Cessna 172 C-GEYG did not stretch their downwind leg to follow the aircraft ahead; the crew may have confused the Cessna 150 C-FNLD, still in the circuit, with the traffic that had just landed, or else was not attentive to the communications that would have allowed them to know what aircraft were ahead. The crew of each aircraft could have seen the other aircraft at several places in the circuit. The pilot of Cessna 150 C-FNLD could have seen Cessna 172 C-GEYG at turning on the base leg and after his turn on the final leg. The pilot of Cessna 172 C-GEYG could have seen Cessna 150 C-FNLD while C-GEYG was on the downwind leg and during its descent on the base leg. Several factors, such as the appearance of the aircraft, the environment, a lack of attention or operation of the radios, could explain the collision, but no single factor could be identified in the investigation. The lack of evasive action by either aircraft indicates that neither aircraft had noticed the other. The landing light of Cessna 172 C-GEYG was on, thereby increasing the possibility of its being identified by Cessna 150 C-FNLD during certain phases of flight. This advantage, however, proved useless when the aircraft were on the final leg, because Cessna 172 C-GEYG was behind and above the Cessna 150. The aircraft collided in flight at an altitude of 450 feet on the final leg for Runway 29 at Mascouche and crashed, although, just before the collision, a pilot on the ground tried to warn them of the danger. The video sequences show that when the aircraft separated there was insufficient altitude available to effect a recovery. Both flight crews were certified and qualified for the flight in accordance with existing regulations. Both aircraft seem to have followed the joining, circuit and communication procedures in effect for an uncontrolled aerodrome. Neither aircraft seems to have reported its position on the base leg, and was not required to do so under existing regulations. Several factors such as the appearance of the aircraft, radio reception, the environment and the lack of crew attention were assessed, but none was identified as a determining factor in the accident. The aircraft collided in flight at an altitude of 450 feet on the final leg for Runway 29 at Mascouche. No evasive action was taken to avoid collision, indicating that neither pilot was aware of the other aircraft's presence. The Cessna 172's pilot does not seem to have taken the presence of the Cessna 150 into consideration when planning his circuit.Findings Both flight crews were certified and qualified for the flight in accordance with existing regulations. Both aircraft seem to have followed the joining, circuit and communication procedures in effect for an uncontrolled aerodrome. Neither aircraft seems to have reported its position on the base leg, and was not required to do so under existing regulations. Several factors such as the appearance of the aircraft, radio reception, the environment and the lack of crew attention were assessed, but none was identified as a determining factor in the accident. The aircraft collided in flight at an altitude of 450 feet on the final leg for Runway 29 at Mascouche. No evasive action was taken to avoid collision, indicating that neither pilot was aware of the other aircraft's presence. The Cessna 172's pilot does not seem to have taken the presence of the Cessna 150 into consideration when planning his circuit. For an undetermined reason, the crew of the Cessna 172 did not maintain safe separation by stretching the downwind leg of the circuit to take the presence of the Cessna 150 into consideration. Several factors such as a failure of the radio equipment, the appearance of the aircraft, the environment and a lack of attention, may have contributed to the occurrence.Causes and Contributing Factors For an undetermined reason, the crew of the Cessna 172 did not maintain safe separation by stretching the downwind leg of the circuit to take the presence of the Cessna 150 into consideration. Several factors such as a failure of the radio equipment, the appearance of the aircraft, the environment and a lack of attention, may have contributed to the occurrence. Since the accident in Mascouche, Transport Canada has delivered several presentations on the subject of circuit procedures at uncontrolled aerodromes. The presentations emphasize the importance of communication to ensure aircraft separation and the use of landing lights to increase the probability of being seen.Safety Action Since the accident in Mascouche, Transport Canada has delivered several presentations on the subject of circuit procedures at uncontrolled aerodromes. The presentations emphasize the importance of communication to ensure aircraft separation and the use of landing lights to increase the probability of being seen.